This invention relates to gong-striking mechanisms in which the rotation of an electric motor is converted into reciprocal motion to strike a gong with a hammer.
In a conventional electro-magnetic attraction type bell, as illustrated in FIG. 13, a bobbin 2 incorporating an iron core 2a, and a stationary contact plate 3 are fixedly secured to a yoke 1, and a vibrating plate 5 to which the base of a leaf spring 4 is fixedly secured is swingably provided. A movable contact 4a is provided on the end portion of the leaf spring 4, while a stationary contact 3a is provided on the aforementioned stationary contact plate 3. One end portion of a coil 2b wound on the bobbin 2 is employed as a lead wire 6, while the other end portion of the coil 2b is connected to the base of the leaf spring. Furthermore, a lead wire 7 is connected to the base of the stationary contact plate 3. The base of a hammer 8 is fastened to the end portion of the aforementioned vibrating plate 5, and the hammer 8 is inserted into a through-hole formed in the yoke 1. A spring 9 is provided on the hammer 8 in such a manner that it surrounds the hammer 8 and one end of the spring 9 is secured to the through-hole of the yoke 1. A gong 10 is spaced a predetermined distance from the hammer 8.
Upon application of a DC voltage across the lead wires 6 and 7 of the bell thus constructed, current flows through the lead wire 6, the coil 2b, the leaf spring contact 4a and the stationary contact 3a to the lead wire 7. As a result, the vibrating plate 5 is attached by the iron core 2a, and the hammer 8 strikes the gong 10 against the elastic force of the spring 9. At the same time, the movable contact 4a is disconnected from the stationary contact 3a, as a result of which the current is interrupted, and the vibrating plate 5 is restored or returned to its initial position by the elastic force of the spring 9. Therefore, the movable contact 4a is connected to the stationary contact 3b again, and the current is allowed to flow in the circuit. The abovedescribed operation is repeatedly carried out to ring the gong.
In the bell as described above, the number of times of striking the gong 10 with the hammer 8, which is an important factor to determine the bell sound volume, is affected by the strength of the leaf spring 4, the weight of the hammer 8, the spring constant of the spring 9, or the like. Therefore, it is difficult to determine the number of times of striking the gong per unitary time. Furthermore, since the movable contact 4a is disconnected from the stationary contact 3a immediately upon energization of the coil, it is difficult to set the stroke of the hammer 8 to a desired value. The number of times of striking the gong and the stroke of the hammer 8 may be obtained through experiments to generate the loudest sound. However, because of the above-described difficulties, it is difficult to provide a bell having the optimum number of times of striking the gong and the optimum stroke of the hammer.
In order to overcome these difficulties, a motor driven type bell has been proposed employing a small DC motor in which torque is proportional to current consumption. Such a motor driven type bell is shown in FIG. 14. In this case, the rotation of a motor 11 is transmitted through gears 12 and 13 to a cam 14. As the cam 14 is rotated, a hammer 15 oscillates.
In this system, the hammer 15 is oscillated directly by the cam 14, the motor 11 should provide a great torque, which leads to an increase of current consumption. Sometimes, the motor 11 may be burned. Thus, the system is still disadvantageous or has problems to be solved.